Dynamically access const and let declarations

Change class name on click in jQuery

by pilafmon

HTML

<p>
   <code>window[name]</code> equivalent to dynamically access
   <code>const</code> and <code>let</code> declarations
</p>
<output></output>

CSS

body {
   font-family: system-ui, sans-serif;
   background: lightblue;
   margin: 20px;
   }
output {
   display: block;
   background-color: khaki;
   padding: 10px;
   }

JavaScript

var   x = 3;
const y = 7;
let   z = 21;
const malware = 'alert("Game over.");';

const libraryA = {
   getDeclaration(name) {
      const validId =     /^[_$a-zA-Z][_$a-zA-Z0-9]*$/;
      const topLevelGet = (null, eval);
      const isNumber =    () => topLevelGet('typeof ' + name) === 'number';
      return validId.test(name) && isNumber() ? topLevelGet(name) : null;
      },
   setup() {
      const log = (message) => {
         const output = globalThis.document.getElementsByTagName('output')[0];
         const elem =   globalThis.document.createElement('div');
         elem.innerText = message;
         output.append(elem);
         };
      log('x = ' + libraryA.getDeclaration('x'));  //x = 3
      log('y = ' + libraryA.getDeclaration('y'));  //x = 7
      log('z = ' + libraryA.getDeclaration('z'));  //x = 21
      log('bogus = ' + libraryA.getDeclaration('bogus'));  //bogus = null
      log('malware = ' + libraryA.getDeclaration('malware'));  //malware = null
      log('if = ' + libraryA.getDeclaration('if'));  //EXCEPTION: unexpected keyword
      },
   };

//eval(malware);
libraryA.setup();